Check the wires in the car to hatch umbilical.
It's a common fault where the wiring insulation gets hard and brittle.
Constant flexing when opening the boot causes the wires to snap inside the insulation, add condensation/rain and you get a short.
You'll want to fix it pretty sharpish or the boot lock solenoid will burn out.
I had this on my old Mk1 and patched the wires with some crimp connectors and a length of spare wire.
You may find that the damaged wire is discoloured black, cut back to a clean copper area.
Check them all as if one has gone them it's likely the others are going/gone too.

Glad to help.
It may be a good idea to let an Auto Electrician have a look, they'll check and replace any damaged wires and shouldn't take more that an hour.
Other symptoms to look out for are intermittent rear wiper not returning to the correct park position, third brake light not functioning and the rear demister not working properly.
I had and needed to cure all these symptoms on my previous car so have intimate knowledge of the problems.

Finally someone with the same issue!! I have had exactly the same problem and its driving me crazy, as soon as i turn my key in the ignition my boot unlocks itself and it wont close unless i take my key out. Its almost like it locks it in an open position.

Ive tried changing the whole lock, checked the fuses including the ignition fuse and they are all fine, ive tried reseting my central locking system but nothing worked! However ive checked my wires and like you say they are damaged, so ill have a look into changing them.

The wiring fault in the boot conduit is a very common occurrence.
I had it myself so can recognise the symptoms instantly.
Took me two replacement wiper motors to figure it out so if I can save others the un-necessary expense of bits that don't need replacing them I'm happy.

Right i managed to change the wire for my boot lock, i got it off a 54 plate focus in a scrap yard, i connected the wires using crimps however the boot still opens when i turn the key in the ignition and wont close again as long as the ignition is still on. I dont know what else it could be !

Although when i open my boot i can hear the lock making an unusual noise, like its trying to lock its self, could it be the lock again ?

Please help its driving me insane ! Hate having a button in the front of my car that doesnt do anything now lol!

Im not to sure, i removed the black tape from around the 3 wires and i traced them as far back until the point i could see no damage because the wire closest to the lock had tears in the insulation and from there i connected the newer wire and still i had no luck.

However i think you may be right with the lock, when i first changed the lock i didnt realise how easy the key cylinder could be removed (as shown in your pdf), because i took the whole lock apart and basically went the long way around and i may have broken it in the process, ill get another lock and let you know my progress lol

Right finally!!! I have acutally managed to fix the problem after going throw 3 boot locks, replacing the wires twice and buying new fuses! All to find that the problem was in my hand, my cars fob was tripping the lock and whenever it was in the ignition it would open my boot.

I noticed at first that when i was driving my doors had a tendency to lock themselves so i took apart my key fob, cleaned it with some contact cleaner and that did it!! Everything works perfectly!

I wish i could say that this solved my problem but unfortunately it hasn't as my car does not have a key fob. i do believe it may just of been the cold affecting the electrics more as i also have the "doors locking themselves" problem but only in cold weather. Now its warmer i thought i would plug the wire back into the boot release motor and all works fine. *just like the doors arn't locking themselves atm*